In most cases, an air-conditioning duct is installed in the ceiling or under the floor of a building by connecting a plurality of duct units to a necessary length. Air-conditioning ducts have a rectangular shape or a circular shape. A duct in rectangular shape is generally called a rectangular duct and has, in principle, button-punch snap locks or Pittsburgh locks in at least two places. For connection of rectangular ducts, an angle connection method or a tee duct connection (TDC) method is used. In the angle connection method, flanges are formed from steel angle members and are rivetted to duct bodies, and the entire peripheral flanges are connected by bolts and nuts. In the tee duct connection method, tee duct connector flanges are made by forming metal sheets metal, corner pieces are attached to the tee duct connector flanges at the time of assembly, and the tee duct connector flanges are connected by bolt and nuts at the four corners and special flange retaining metal fittings (clamps or the like).
Conventional duct units have a blank thickness of 0.4 to 1.6 mm after a preservative treatment and have a longer side length of ordinarily 2000 mm or less, and a width in the range from 150 to 3000 mm. Metal sheets with connection flanges are assembled into a tubular shape in a factory in advance to form such duct units, and the duct units are transported to a workplace by container transportation using a truck with care not to deform the duct units.
In ordinary cases, the length of the longer side of such duct units is not larger than the width of the blank metal sheet because its maximum value is ordinarily limited to the width of a metal sheet roll. On the other hand, the duct units are designed so that the width in the transverse direction is set to a value in the above-mentioned range according to the ventilation amount. In the case of large duct units, therefore, the number of duct units a truck can carry is only a limited part of the total number of duct units. In such a case, the transportation efficiency is considerably low and the cost of transportation of duct units is large. Moreover, the amount of carbon dioxide exhaust considered a main cause of global warming is not negligible due to considerably low energy efficiency. In construction of high-rise buildings increasing in number recently, a substantial space is required for carrying-in of duct units, a substantially long time is required for lifting, and the cost of transport inside and outside the buildings are large.
Therefore, an object of the present invention to provide, as a solution to the above-described problem, an air-conditioning duct unit which can be made compact during transportation to effectively reduce the costs required for truck transportation and transport inside and outside a building and to contribute to a reduction in the amount of carbon dioxide exhaust.